The present invention relates to a continuous cooking apparatus i.e. a continuous digesting apparatus for digesting a high viscous material such as a raw material for bean curd (for example, a Japanese food "tofu") of various kinds of soups.
In general, it is called as "cooking" or "digesting" to gradually and uniformly heat from the room temperature to about 100.degree. C. the high viscous material such as the raw material for "tofu" which is made from soybeans by grinding sodden soybeans or by watering powdered soybeans or pressed soybeans.
Heretofore, there has been used many digesting apparatus and heating apparatus and one of which is disclosed in Japanese Patent Publication No. 22,940/1986. The digesting apparatus of this Japanese Patent has a screw-conveyor shaped baffle plate and therefore the raw material fed to the digesting apparatus is passed therethrough without being subjected by any agitating and mixing action. This causes an uneven digestion due to difference in degree of digestion between the raw material near the steam cylinder and that away therefrom. Accordingly, it is impossible to manufacture "tofu" having excellent taste and construction. In addition, the digesting apparatus of this prior art has disadvantages that it cannot remove the bitterness such as saponin from the raw material by generating bubbles in the raw material and by discharging the bitterness constituent together with the bubbles since the digesting pipe of this apparatus is formed as a closed system and thus no outlet of the bubbles is formed in the apparatus.
Disclosed in Japanese Patent Publication No. 2,391/1971 is another digesting apparatus in which no baffle plate is provided in the steam cylinder. Accordingly, the raw material is passed through the apparatus without being subjected by any agitating and mixing action and therefore uneven digestion is caused therein. In addition, bubbles are formed in this apparatus by steam injected from a steam injecting pipe without being mixed with the raw material and the bubbles thus formed rise upward and are then discharged from an air drain pipe. This lowers the heating efficiency of this apparatus.
Other digesting apparatus of the prior art are disclosed, for example, in Japanese Laid-open Patent Publication No. 48,673/1973 and Japanese Patent Publication No. 22,940/1986. In these apparatus, since steam injecting apertures are uniformly arranged over the entire region of a steam injecting pipe, it is impossible to maintain the temperature of the raw material constant while the raw material is passed through the steam injecting pipe. Accordingly, the rapid increase of temperature is caused when the injection of steam is strong and on the contrary sufficient agitation and mixture of the raw material cannot be carried out when the injection of steam is weak. This causes the uneven digestion of the raw material and therefore lowers the taste of the finished food, for example: "tofu".
In these digesting apparatus of the prior art, the digestion is generally carried out by the centrally arranged steam injecting pipe having steam injecting apertures uniformly arranged over the entire region thereof. However, even if reducing the number of the steam injecting apertures toward the downstream side of the steam injecting pipe, the pressure and the temperature acting on the whole raw material would become always equal in any portion of the raw material due to the steam injected from a steam injecting pipe arranged downstream side. Also, the control of the temperature and the pressure acting on the raw material is carried out simultaneously and uniformly in every digesting chambers (compartments) although an individually independent control is required to each digesting chamber according to the degree of digestion i.e. the integrated residence time of the raw material in the digesting chambers. Excessive heat of the raw material is undesirable especially in the leaching of protein from the raw material.